If you plan on riding it for fitness as well as lugging stuff, definitely get the LHT. The Big Dummy is really designed as a cargo bike and pretty much only a cargo bike; i'd only go that route if you plan on 90%+ of your rides to be hauling major cargo (not just groceries, etc).

The nice long chainstays on the LHT (compared to a traditional road bike) mean you can fit pretty big panniers on the back and not have to worry about heel strike, but it's still a "normal bike" and rides like one. It's not the snappiest, fastest thing in the universe, but it's crazy stable and handles loads really well.